This 28mm f/2.8 MC Auto-Beroflex lens is a relatively small M42 mount lens featuring a maximum magnification ratio of 1:4 (higher magnification than a Sigma mini-wide which only goes to 1:6). While not exceptional, quality is quite good. Considering its low price, this is a very nice lens.

Here are a few shots from the "Porst color reflex mc auto" 55/1.2 lens, in Pentax K mount. This lens is built by Cosina, and features 6 optical elements in 6 groups (so it is different from the 55mm f/1.2 Tomioka lens in M42 mount which features 7 elements in 6 groups). Oddly, its aperture ring does not feature any stop between f/1.2 and f/2. All the shots are wide open (ie f/1.2)

In daylight, when shooting wide open this lens exhibit some kind of dreamy behavior:

At night, it does not exhibit this dreamy/fuzzy look unless there is significant light on the subject in focus:

The Zenitar M2s is a very surprising lens. Designed to be a cheap replacement for Helios 44-x lenses as a kit lens for Zenit DSLRs, is a 50/2 lens in a fully plastic barrel (although some internals are made of metal). This plastic housing is really a pity, as it gives it a cheap look and feeling.

However, from an optical point of view, it is really surprising. A smooth bokeh wide open, quite robust against flare and very sharp once stopped down (even if wide open sharpness is already quite good). Krasnogorsky Zavod (the manufacturer) rates it as able to resolve 65/40 l/mm, while the supposedly very sharp MC Helios 44M-7 is only rated as able to resolve 50/30 l/mm.

It is available under the "Zenitar M2" and "Zenitar M2s" labels for the m42 version, and "Zenitar K2" for the K mount version:KMZ page about this lens